Disclosed are a heat exchanger and a method of manufacturing a heat exchanger. The heat exchanger may include a plurality of three-step tubes, each having a three-layered section and each having a liquid passage at a middle portion and module insertion spaces at opposite sides of the liquid passage, a plurality of thermoelectric modules inserted into the module insertion spaces, a plurality of cooling fins coupled to an outer surface of each of the three-step tubes, and an upper tank and a lower tank coupled to an upper side and a lower side of the three-step tubes to be fluidically communicated with the liquid passages of the three-step tubes. The three-step tubes and the cooling fins may be stacked laterally with respect to each other. The three-step tubes, the cooling fins, the upper tank, and the lower tank may be brazed by a same filler material comprising a metal.